This invention relates to an apparatus for cutting a long intermediate product in the form of a continuous bar, for example, an intermediate cigarette product, into individual products, such as cigarettes. More particularly, it relates to such an apparatus including a cutter head supported rotatably on a rotary shaft, a knife projecting from the cutter head, and means provided in the cutter head for holding the knife and moving it to its cutting position.
There is known a machine which is used for making a long intermediate product in the form of a continuous bar and cutting it into individual products. A typical machine of this type is used for the manufacture of, for example, cigarettes. The quality of the cutting work is a matter of critical importance in the manufacture of cigarettes. The sharpness of a cut end surface is one of the important factors which determine the outward appearance of cigarettes. If a cigarette has an uneven cut surface, it prevents any satisfactory bonding of a filter tip thereto, or is automatically rejected during a gas permeability test. In either event, the production efficiency of the machine is lowered accordingly.
In a cigarette making machine, the cutting work is usually performed by an apparatus which comprises a cutter head supported rotatably on a rotary shaft, and a knife projecting from the cutter head. The knife is formed from a flat plate and has a cutting edge at its outer end. The knife is removably supported by a knife holder which is provided in the cutter head. The knife holder is provided with means for advancing the knife radially of the axis of rotation of the cutter head. The cutting edge lies on a segment of a curve having a progressively increasing distance from the axis of rotation of the cutter head, and has an eccentric contour along which it can progressively cut into a cigarette bar. When the knife is moved across a cigarette bar to cut a cigarette therefrom, its contact surface is shifted at the same speed as that at which the bar travels.
The knife is ground when it is in another position during its rotation. A grinding stone is disposed on the path of movement of the knife to grind its cutting edge. The grinding work not only means the grinding of the cutting edge, but also substantially defines its position relative to a cigarette bar. The work of advancing the knife makes up for the wear of its cutting edge which results from its cutting operation. In practice, the knife is advanced to a greater extent than is required to make up for the wear of its cutting edge, so that it may be forcibly ground to maintain a sharp edge.
The knife is usually advanced at a very low rate. A typical knife which cuts one cigarette during each rotation of the cutter head is advanced at a rate of 1.5 to 2 mm per hour when the cutter head is rotated at a speed of 2500 to 4000 rpm, and at a rate of, say, 3 to 3.5 mm per hour even if the cutter head may have a rotating speed of 5000 to 8000 rpm.
There have, however, been only a few technical proposals concerning the means for advancing the knife, and practically similar means have always been adopted. A typical known means for advancing the knife is shown in, for example, U.S. Pat. No. 3,518,911. It described two typical examples with reference to the drawings.
According to one of those examples, the cutting apparatus includes a knife for cutting a longitudinally traveling continuous cigarette bar, and a cutter head having an axis of rotation inclined at an angle to the longitudinal axis of the bar. This inclination gives the knife a component force of motion toward the bar. The cutter head is rotatably supported on a Cardan joint.
The knife holder is movable along a threaded pin which extends radially of the cutter head. The pin is rotatable about its own axis by a gear transmission mechanism and its input end is provided with a ratchet. A swing lever extends from the center of the rotary shaft about which the cutter head is rotatable, to the ratchet and is provided at one end with a pawl engaging the ratchet. A rod extends coaxially with the rotary shaft slidably therethrough and has one end connected to the other end of the lever. The other end of the rod faces the armature of an electromagnet so that the rod may be attracted whenever the electromagnet is energized. The swinging motion of the lever is transmitted to the gear transmission mechanism through the ratchet to rotate the threaded pin so that its screw motion may advance the knife.
According to the other example, a pawl is provided at one end of a rod extending coaxially and slidably through the shaft about which the cutter head is rotatable, and engages a ratchet to rotate a gear shaft of which the rotation is transmitted to a threaded pin. A worm and a worm screw are employed for advancing the knife. Further details of the apparatus of the type according to this example are shown in, for example, U.S. Pat. No. 3,176,560.
While the conventional apparatus as hereinabove described employs a Cardan joint for supporting the cutter head, it does not follow that only a Cardan joint can be employed in a cigarette cutting apparatus. It is true that the use of a Cardan joint is advantageous from the standpoint of, for example, altering the cut length of cigarettes, or positioning the grinding stone for the knife. In view of the importance of disposing the axis of rotation of the cutter head at an angle to the longitudinal axis of cigarettes, however, a cutting apparatus having an inclined shaft is already in practical use. The conventional apparatus having an inclined shaft or an inclined cutter head, however, employs for advancing the knife the means which does not differ from what is disclosed in the patent specifications as hereinabove referred to.
When the rod is attracted by the energized electromagnet, its axis displacement is transmitted to the ratchet through the lever or directly to rotate the threaded pin, though the rod can also be driven manually, or by a cam or any other appropriate mechanical device. The rotation of the ratchet is transmitted to the threaded pin through the gear transmission mechanism or directly and its screw motion advances the knife which is integrally held on a nut fitted about the pin. Alternatively, the rotation of the ratchet is transmitted to the worm screw for advancing the knife.
If the cutter head is rotated at a high speed, a large centrifugal force and a large force of inertia act on its elements, and the cutting of cigarettes or the grinding of the knife, for example, exerts on the cutter head an impact which resists its rotation to some extent. Therefore, a gradient of frictional resistance is taken into account in the selection of the screw thread, or worm which is used for advancing the knife. Neither the screw nor the worm, however, provides a sufficiently large ratio of speed reduction to achieve a very low rate which is desired for the advance of the knife.
Therefore, it has been usual to control the interval of energization of the electromagnet to, for example, one minute, to delay the advance of the knife, or provide a train of reduction gears between the ratchet and the threaded pin. According to the conventional apparatus, therefore, the knife is advanced substantially intermittently at a very low rate on the average so as not to create any impact when it is advanced. The knife appears to be continuously advanced and ground, but in substance, it is intermittently advanced to be brought into contact with the grinding stone, or cut a cigarette.
Although these features of the conventional apparatus have so far not caused any actual trouble, there is every likelihood of the knife receiving an unduly large impact upon contacting the grinding stone, or of a cigarette having an uneven cut surface. It is feared that an increase in the operating speed of the cutting apparatus may result in the actualization of any such trouble.
Moreover, if a train of reduction gears is employed for controlling the rate at which the knife is advanced intermittently, it adds to the number of the parts located in the cutter head and thereby increases the inertia on the rotating cutter head. This makes it difficult to rotate the cutter head at an increased speed. Such is particularly the case if the gear train is spaced apart from the center of the shaft about which the cutter head is rotatable.